Cellular components of the immune system, including cytotoxic T cells, macrophages and natural killer cells, are capable of the direct destruction of a variety of target cells including allogeneic cells and virus-infected or malignant cells within the host individual. Research on these cellular cytotoxicity reactions, their modulation in a variety of disease states and their regulation by a number of natural and synthetic substances is being vigorously pursued in laboratories throughout the world. To date, cellular cytotoxicity reactions are monitored almost exclusively by the 51Cr-release microcytotoxicity assay, which is expensive and time-consuming. We propose to develop a simple, rapid, and relatively inexpensive nonisotopic assay for cellular cytotoxicity reactions based upon quantitation of intracellular antigens released from damaged target cells in an enzyme immunoassay. In Phase I, we will prepare polyclonal antisera to cytosol preparations from human leukocytes and certain human cell lines. The IgG fraction of the antisera will then be conjugated to horseradish peroxidase or beta-galactosidase. Enzyme immunoassay cytotoxicity (EIC) reactions employing these reagents and human natural killer cells or cytotoxic T cells generated in in vitro mixed lymphocyte cultures will be compared to standard 51Cr-release method. If the sensitivity specificity and linearity of EIC reactions prove comparable or superior to those of 51Cr-release assays, the goal of Phase II research will be determination of the best combination(s) of antisera, enzyme, substrate, transfer mechanism, buffers, and packaging for an EIC kit (or kits) that is sufficiently simple, sensitive and quantitative for use in the routine clinical monitoring of cellular immune function.